Polymer mixtures comprising polyvinyl chloride, an aromatic polycarbonate and a rubber like polymer are known from German Patent Application No. 23 04 894 and German Patent Specification No. 24 02 176. German Patent Application No. 23 04 894 describes polymer mixtures comprising polyvinyl chloride, an aromatic polycarbonate preferably having a molecular weight from 20,000 to 60,000 and an ABS graft copolymer, a styrene maleic acid anhydride copolymer or an ethylene vinyl acetate copolymer. These known polymer mixtures, in as far as they comprise a rubber like polymer, are always prepared by first softening the polyvinyl chloride together with the ABS graft copolymer or the ethylene vinyl acetate copolymer after which plasticized polycarbonate is added.
The disadvantage of this method is that the polyvinyl chloride comes in contact with a plasticized polycarbonate mass having a temperature of approximately 250.degree. C. At this temperature, thermal decomposition of polyvinyl chloride occurs and in the case of short contact times and the use of polyvinyl chloride stabilizers. German Patent Specification No. 24 02 176 describes polymer mixtures on the basis of polyvinyl chloride and a polycarbonate which may comprise a rubber or a rubber modified thermoplastic polymerisate. According to this prior art, polycarbonates having a weight averaged molecular weight from 20,000 to 80,000 are preferably used. As a rubber modified thermoplastic polymerizate are preferably used rubbers on the basis of polybutadiene or butadiene copolymerizates.
These known polymer mixtures can be prepared by dissolving the polymeric constituents in suitable solvents and evaporation or coprecipitation. According to this prior art it is also possible to mix the constituents mechanically. According to this German Patent Specification the rubber in the polymer mixtures forms a natural phase which is finely divided in the polymer mixture.
The invention provides a method of preparing polymer mixtures comprising polyvinyl chloride, an aromatic polycarbonate and a rubber like polymer, in which thermal decomposition of the polyvinyl chloride is prevented.